Many data processing algorithms require comparison analysis of raw data in order to provide a dataset that is refined, filtered, or enhanced for further processing. For instance, data retrieves from image capturing devices may need to be processed to, for example, provide a clear image, detect objects in the image, or provide higher resolution.
An example of an image capturing device is a Synthetic Aperture Radar (SAR) sensor. In a way, SAR is like a camera. However, rather than using light to create an image, SAR relies only on radar signals it sends out. This allows SAR to produce images in total darkness. SAR also takes advantage of radar's penetrating ability, allowing it to “see” through clouds, rain, snow, and fog. Generally, creating a SAR image involves mounds of data and tremendous computing power.
In general, a SAR antenna (from an airplane) sends out pulses of high-frequency radio waves (radar waves) toward the ground. In between the pulses, the antenna receives “backscatter”—radar waves that have bounced off objects on the ground. All backscatter pulses hold information, including how long each pulse took to make the round trip to and from the plane and if the SAR antenna is moving toward or away from the object on the ground.
From the travel time of each radar pulse a computer can calculate the distance to the object it bounced off, and from the time interval between adjacent pulses it can calculate how fast the pulse was moving toward or away from the object. The computer now has to figure out, from all the data it has stored, which pulses have bounced back from the same location. It does this by looking for a pattern. The computer is programmed to know that if an object is moving closer and closer at a set rate (and then farther and farther away at a set rate), then the time interval between pulses should also change at a set rate.
When the computer determines, from the vast amount of pulse data stored, certain pulses that fit a specific pattern, the computer knows that these pulses bounced off the same location (object) on the ground. Based on accurate knowledge of sensor position at the time the pulses that fit the pattern were sent and received, the computer determines the coordinate of the object on an image of a scene associated with the object being created by the computer.
Although, the object's coordinate on the image is determined, the brightness of the object is still not known. SAR determines the brightness by the intensity of the signal it receives. An object such as a tree absorbs some of the radar energy and so it appears gray. A metal object oriented toward the SAR antenna reflects a lot of the energy back, so it appears bright.